The invention relates to vehicles heading four-wheel steering. Particularly, the invention relates to lawn and garden tractors having four-wheel steering.
It is known to provide lawn and garden tractors with four steerable wheels to thereby decrease the tractor""s minimum turning radius. One such four-wheel steering system is described in U.S. Pat. No. 5,174,595. This patent describes a tractor that has a frame and front and rear pairs of wheels for supporting the frame. The front and rear pairs of wheels are pivoted to steer the tractor. Front and rear center-pivot members are pivotally carried by the frame at respective points located proximate the centerline of the tractor.
Each front tie rod of a pair of front tie rods extends respectively between the front center-pivot member and the front wheels for pivoting the front wheels as the front center-pivot member pivots. Each rear tie rod of a pair of rear tie rods extends respectively between a rear center-pivot member and the rear wheels for pivoting the rear wheels as the rear center-pivot member pivots. A linkage assembly operatively couples the front and rear center-pivot members for transmitting pivotal motion therebetween.
The linkage assembly includes a first rod member coupled with the front center-pivot member. A first swing member is swingably carried by the frame and is coupled with the first rod member for swinging about a vertical axis as the front center-pivot member pivots. A second rod member couples the first swing member with a second swing member. The second swing member is carried by the frame for pivotal motion about a generally horizontal axis. A third rod member is coupled between the second swing member and the rear center-pivot member. The front portion of the second rod is restricted from shifting vertically, since the first swing member pivots about a vertical axis.
This four-wheel steering design is relatively costly to manufacture. Furthermore, the use of a front center-pivot member can restrict the available under-carriage space for use by a mower deck or traction components of the tractor. The present inventor has recognized that there is a need for a less costly, less complicated, and less bulky, four-wheel steering system for a utility vehicle, particularly for a lawn and garden tractor.
The invention provides a four-wheel steering system for a utility vehicle that includes a frame; a pair of front wheels rotationally mounted with respect to the frame via a pair of front pivotal wheel support assemblies to be pivotal about respective turning axes for steering; a pair of rear wheels rotationally mounted with respect to the frame via a pair of rear pivotal wheel support assemblies to be pivotal about respective turning axes for steering; a hydraulic cylinder connected at one end thereof with respect to the frame and at an opposite end thereof with respect to one of the front pivotal wheel support assemblies at a radial distance from its respective turning axis, and operable to expand and contract to pivot the one front pivotal wheel support assembly; and a linkage assembly operatively connected between one of the front pivotal wheel support assemblies and the rear pivotal wheel support assemblies to transform pivoting motion of the front pivotal wheel support assembly to pivoting motion of the rear pivotal wheel support assemblies in an opposite rotational direction to the pivoting motion of the front pivotal wheel support assembly.
One exemplary embodiment of the four-wheel steering system of the invention is described herein. A frame carries a pair of front wheels that are rotationally mounted to the frame via an axle and a pair of front pivotal wheel support assemblies. For steering, the front pivotal wheel assemblies are pivotal with respect to the axle about respective turning axes. The frame also carries a pair of rear wheels that are rotationally mounted to the frame via a pair of rear pivotal wheel support assemblies. For steering, the rear pivotal wheel assemblies are pivotal with respect to the frame about respective turning axes.
Each of the front pivotal wheel support assemblies includes a front steering arm extending radially from the turning axis of its respective front pivotal wheel support assembly. A front axle tie rod is pivotally connected at opposite ends thereof to each of the front steering arms at a radial distance from each respective turning axis of the front pivotal wheel support assemblies. The tie rod causes the front steering arms to pivot together. A hydraulic cylinder is connected at opposite ends thereof to the axle and to one front steering arm at a radial distance from its pivot axis, and is operable by steering input from an operator to expand or contract to selectively pivot the front steering arms.
Each of the rear pivotal wheel support assemblies includes a rear steering arm extending radially from the turning axis of its respective rear pivotal wheel support assembly. A linkage assembly is operatively connected between one of the front steering arms and the rear steering arms to transform pivoting motion of the front steering arm to pivoting motion of the rear steering arms in an opposite rotational direction to the pivoting motion of the front steering arm.
The linkage assembly includes: a front intermediate pivot, a front intermediate link, a longitudinal rod, a lever, a rear intermediate link, a rear pivot member, and first and second tie rods. The front intermediate pivot is mounted for pivoting with respect to the frame. The front intermediate link is pivotally connected at opposite ends thereof to the one front steering arm and to a pivot joint on the front intermediate pivot. The longitudinal rod is pivotally connected at a first end to the front intermediate pivot. The lever is pivotally mounted to the frame, and the rod is pivotally connected to the lever. The rear pivot member is pivotally mounted to the frame. The rear intermediate link is pivotally connected between the lever and the rear pivot member. The first and second rear tie rods are each connected at respective first ends to the rear pivot member and at respective second ends to respective rear steering arms.
The inventive four-wheel steering eliminates the need for a front center-pivot which reduces the cost, bulk and complexity of the four-wheel steering system.